There is considerable evidence that breast feeding is medically, nutritionally and psychologically the best method of feeding human infants. Of particular importance from the perspective of infant health is the relatively low incidence of breast feeding among less well-educated, poor and minority women. Despite the importance of breast feeding for infant health, little data exist on those factors that influence breast feeding behavior and on why so few breast feeders continue nursing beyond the early postpartum weeks. The specific aims of this study are: (1) to determine the rates of adoption and duration of breast feeding in different racial and education groups; (2) to use alternative causal modeling techniques to identify the determinants of breast feeding; (3) to determine the factors which account for the different rates of breast feeding observed in different education and racial groups; and (4) to determine whether there are differences in the factors which underlie initiation of breast feeding, and duration and cessation of breast feeding. Nine-hundred-fifty-two women will be studied in a six group, 2 x 3 prospective design in which the sample will be stratified by two levels of race and three levels of education. With one exception, mothers will participate in one prepartum and three postpartum interviews; a sub-sample of women will receive the three postpartum interviews only. A 50% random sample of "significant others" will receive one prepartum interview. Variables to be studied were drawn from the atheoretical empirical literature on infant feeding and social psychological theory on the determinants of social behavior, most notably Fishbein's model. Variables have been organized into a conceptual framework including five groups of factors: attitudes and beliefs, habits and modeling, non-volitional factors, normative pressures and social support, and sociodemographic characteristics. Analytical strategies include sampling theory methods for estimating rates, regression-analysis of variance techniques, and complex causal modeling with structural education models.